Dual cure emulsions

ABSTRACT

The invention concerns an aqueous polymer dispersion composition comprising for 100 parts by weight of (A)+(B):(A) from 30 to 99 parts by weight of at least one dispersed polymer containing acetoacetoxy-type functional moieties, the said polymer having a glass transition temperature from 0 to 100° C.; and (B) from 1 to 70 parts by weight of a multifunctional acrylate, said aqueous composition further containing a volatile base in an amount sufficient to convert the acetoacetoxy functionalities of (A) to enamine ones. The invention does also concern a process of preparation, a coating composition comprising the said composition as a binder, its uses in industrial coatings and a dual cure process of coating.

The present invention relates generally to aqueous polymer dispersioncompositions which are curable by exposure to radiation. Such aqueouscompositions are useful in coatings, particularly in wood and plasticones, plus inks and overprint varnishes. The present invention relatesparticularly to such radiation-curable compositions having a secondarycuring mechanism which is not dependent upon exposure to radiation.

These aqueous polymer compositions comprise for 100 parts by weight of(A)+(B):

-   (A) from 30 to 99, preferably from 50 to 97, parts by weight of at    least one dispersed polymer containing acetoacetoxy-type functional    moieties, the said polymer having a glass transition temperature    from 0 to 100° C. ; and-   (B) from 1 to 70, preferably from 3 to 50, parts by weight of at    least one multifunctional acrylate, preferably pre-dispersed in    water,    said aqueous composition further containing a volatile base in an    amount sufficient to convert the acetoacetoxy functionalities of (A)    to enamine ones. The said acetoacetoxy groups are pending groups    (attached to the polymer backbone) with general formula (I):    wherein    -   y is 0 or 1; and    -    preferably a C₂-C₄ alkylene radical.

There is an increasing need for high performance coatings free fromvolatile organic compounds (VOC). In the particular field of IndustrialWood Finishing, VOC free, tack free before curing, open pore mattradiation curable coatings are difficult to obtain with the existingradiation curable systems.

Radiation curable dispersions with these properties are thereforedesired for many applications. On the other hand, other market demandsfor these kinds of coatings are: non-Xi labelling (skin non-irritationor sensitization), good sandability and high chemical resistanceperformances for the final coating, besides good filmification andcoalescence performances in the absence of any coalescing agent for theaqueous dispersion of the invention.

EP-A1-0 486 278 discloses radiation curable dispersions which contain anon-radiation curable emulsion polymer and radiation curablemeth(acrylates). EP-A2-0 736 573 discloses blends of non-radiationcurable emulsion polymers having different Tg and radiation curablemeth(acrylates).

With these dispersions the above mentioned requirements are not yetsatisfactorily met.

It is an object of the present invention to provide radiation curableaqueous polymer dispersion compositions with low VOC, enabling theobtention of coatings without tack before radiation curing and with goodsandability, high chemical resistance and good hardness performancesafter radiation curing besides good filmification performances of thesaid composition in the absence of coalescing agents.

In many aspects of the final coating performances, these compositionsfulfill those of polyurethane dispersions for industrial finishing ofwood surfaces, with the additional advantages to be significantly easierto obtain, less expensive and more environmentally friendly.

We have found that this objective is achieved by the aqueous compositionas defined according to the present invention.

In an additional preferred embodiment, the novel aqueous polymerdispersion composition comprises:

-   60-95 parts by weight of at least one dispersed polymer (A) as    defined above; and-   5-40 parts by weight of at least one pre-dispersed multifunctional    acrylate (B).

The stated weights are based on 100 parts by weight of (A)+(B).

The presence of a volatile base is essential in an amount sufficient toconvert the acetoacetoxy moieties of at least one polymer (A) intoenamine ones.

In case where the polymer (A) contains acidic carboxy groups, the amountof the volatile base must be sufficient to neutralize these acidicgroups and to convert the acetoacetoxy groups into enamine ones.

The conversion of the acetoacetoxy functions of polymer (A) to enamineones enables an efficient chemical blocking of the acetoacetoxyfunctions and to prevent their hydrolysis, which hydrolysis can renderthem ineffective regarding their participation in secondary curingmechanism according to the present invention.

According to the conditions of the present invention (presence of avolatile base), this chemical blocking of acetoacetoxy functions isreversible under drying conditions (evaporation of the base with water),thus enabling a regeneration of the acetoacetoxy functions for anefficient participation in the secondary curing reaction (Michaeladdition reaction) with a part of component (B) before the finalradiation curing.

The acetoacetylated (bearing acetoacetoxy functions) polymer (A) has acontent of acetoacetoxy functions from 0.0047 to 2.8, preferably from0.14 to 1.87, and more preferably from 0.23 to 1.40, expressed in mmolper g of polymer (A). It may also bear acidic carboxy functions,corresponding to an acid value from 0 to 50, with this acid valueexpressed in mg of KOH per g of polymer (A).

Such a polymer (A) and the resulting aqueous polymer dispersioncomposition (comprising (A)+(B)) may be obtained by various methods suchas:

-   (a) by an aqueous emulsion free-radical polymerization of a suitable    monomeric composition comprising besides other monomers, at least    one monomer bearing the acetoacetoxy groups and optionally at least    one monomer bearing acidic carboxy groups. At the end of the    emulsion polymerization, the volatile base is added in an amount    sufficient to convert the acetoacetoxy groups into enamine ones (by    pH adjustment). The aqueous polymer dispersion of polymer (A) may be    used as such or after adjusting the solids content (dilution) if    required before mixing with component (B) as such (to be dispersed)    or in the predispersed form of an aqueous dispersion of (B);-   (b) by a solution or bulk free-radical polymerization of the    suitable monomeric composition as specified in (a), followed by its    dispersion in water, in the presence of the volatile base in an    amount sufficient to convert the acetoacetoxy groups into enamine    ones. This aqueous dispersion can be used as in method (a) for    preparing the final aqueous polymer dispersion of the invention    (comprising (A)+(B)) ;-   (c) by transesterification reaction, in solution and in the presence    of a suitable transesterification catalyst, of a mixture of a    hydroxylated polymer (OH functionality of at least 2), with a C₁-C₄    alkyl acetoacetate, thus enabling the incorporation of acetoacetozy    groups in the said hydroxylated polymer. The aqueous dispersion of    this polymer can be prepared under such conditions as disclosed for    method (b), before introducing component (B), pre-dispersed in water    or to be dispersed in the dispersion of (A);-   (d) by mixing at least two aqueous dispersions of polymers (A), each    one being obtained by one of methods (a) or (b) or (c) and then    introducing component (B), as discussed above.

The polymer (A) as obtainable by methods (a) or (b) may be derived froma monomeric composition comprising for 100 weight parts of components(i)+(ii):

-   (i) 40-99.9, preferably 60-97, and more preferably 70-95, parts by    weight of at least one main monomer selected from the group    consisting of C₁-C₂₀ alkyl (meth)acrylates, vinyl esters of    carboxylic acids of 2 to 20 carbon atoms, ethylenically unsaturated    nitrites of 3 to 6 carbon atoms, vinylaromatics of up to 20 carbon    atoms, vinyl halides, aliphatic hydrocarbons having 2-5 carbon atoms    and one double bond, e.g. ethylenic unsaturation.-    Preferred main monomers of type (i) are: C₁-C₈ alkyl    (meth)acrylates, such as methyl (meth)acrylate, ethyl    (meth)acrylate, n-propyl and isopropyl (meth)acrylate, n-butyl    (meth)acrylate and 2-ethyl-hexyl (meth)acrylate, vinyl esters such    as vinyl acetate and vinyl propionate, styrene and α-methylstyrene    as vinylaromatics, vinyl halides, such as vinyl chloride or    vinylidene chloride, and butadiene and isoprene as diolefins.-    Particularly preferred main monomers are C₁-C₈ alkyl    (meth)acrylates and styrene as well as mixtures thereof;-   (ii) at least one acetoacetoxy functional monomer which may be    present in an amount of 0.1-60, preferably 3-40, more preferably    5-30, parts by weight.-    Acetoacetoxy functional monomers useful for the introduction of    acetoacetoxy functionality may be selected from the group consisting    of acetoacetoxyethyl acrylate, acetoacetoxypropyl methacrylate,    allyl acetoacetate, acetoacetoxybutyl methacrylate, 2,3-di    (acetoacetoxy)propyl methacrylate and the like. In general, any    polymerizable hydroxy functional monomer can be converted into the    corresponding acetoacetate by reaction with diketene or other    suitable acetoacetylating agents.-    A particularly preferred ethylenically unsaturated    acetoacetoxy-type functional monomer is    acetoacetoxyethylmethacrylate (“AAEM”);-   (iii) 0 to 5, preferably 0 to 3, parts by weight of at least one    crosslinking monomer.-    Typically, these monomers crosslink during polymer formation    without requirement of any curing technique. Such crosslinking    monomers can be selected for example from ethylene glycol    diacrylate, ethylene glycol dimethacrylate, allyl methacrylate and    hexanediol diacrylate;-   (iv) 0-5, preferably 0 to 3, parts by weight of at least one    alpha-beta ethylenically unsaturated carboxylic acid or anhydride.-    It may be selected from (meth)acrylic acid, maleic acid or    anhydride, itaconic acid.-    More preferably it is acrylic or methacrylic acid.

The nature and proportions of the monomers (i) to (iv) of which thepolymer may be composed are chosen so that the polymer has a glasstransition temperature from 0 to 100° C., preferably from 5 to 90° C.,and more preferably, from 20 to 90° C.

According to method (c), the polymer (A) may be a modified hydrozylatedpolymer, which is modified by transesterification of C₁-C₄ alkylacetoacetate. Such hydroxylated polymers with OH functionality of atleast 2 may be selected from polyesters, polyetherpolyesters, polyester-and polyether-polyurethanes.

According to methods (a) or (b), the polymer can be prepared by solutionpolymerization or bulk polymerization with subsequent dispersing inwater or by emulsion polymerization. Emulsion polymerization is thepreferred one.

In the emulsion polymerization, the monomers can be polymerized in aconventional manner or in a multistage process, with possibility ofcore/shell structures, in the presence of a water soluble initiator andof an emulsifier, preferably at a polymerization temperature rangingfrom 30° C. to 95° C. The polymer can be also a blend of emulsions ofindividually formed polymers. In case of core/shell structure theacetoacetoxy groups may be present in both shell and core, at the sameor different content, but in the range of the invention as definedabove. The core and shell may have different Tg, but with each one beinginside the range of Tg as defined above for the invention (0-100° C.

At the end of the process, the neutralization step must be carefullycarried out by adding sufficient quantity of volatile base, preferablyammonia, in order to reach a stable pH>7.5 up to 10 and to assure theenamine formation by reacting the volatile base with the acetoacetoxyfunctionality.

Examples of suitable initiators are sodium persulfate, potassiumpersulfate, ammonium persulfate, tert-butyl hydroperoxide, water-solubleazo compounds and redox initiators.

Examples of emulsifiers used are alkali metal salts of relativelylong-chain fatty acids, alkyl sulfates, alkyl sulfonates, alkylatedarylsulfonates or alkylated diphenyl ether sulfonates. Other suitableemulsifiers are reaction products of alkylene oxides, in particularethylene oxide or propylene oxide, with fatty acid alcohols, fatty acidsor phenol or alkylphenols.

In the polymerization, regulators may be used for adjusting themolecular weight. For example, —SH— containing compounds, such asmercaptoethanol, mercaptopropanol, thiophenol, thioglycerol,thioglycolates, methyl thioglycolate, tert-dodecyl mercaptan andn-dodecyl mercaptan are suitable.

The novel aqueous composition contains a multifunctional acrylate (B)which may or may not be emulsified in the water of the polymer (A)dispersion. When so emulsified, it may be emulsified with the aid ofsurfactants as discussed above suitable in an emulsion polymerizationprocess.

A wide variety of multi-functional acrylates having an acrylatefunctionality of at least 2, may be employed. They can be monomeric oroligomeric (up to Mn of 20000) or polymeric (up to Mn 10000). Ifpolymeric ones are used then at least one monomeric one is present with.

The meaning of acrylate is restricted to acrylate function. Typicalexamples include:

-   1—Epoxy acrylates-   2—Urethane and polyurethane acrylates-   3—Multi-functional acrylate monomers-   4—Amine-acrylate adducts-   5—Polyester acrylates-   6—Polyalkoxylated and polyether acrylates-   7—Acrylated acrylic oligomers-   8—Acrylated SMA or S (M) AA (styrene-maleic anhydride or    styrene-(meth)acrylic acid oligomers).    1—Epoxy acrylates are those products formed by the reaction of    acrylic acid with an epoxy (glycidyl) functional component e.g.    aliphatic and aromatic containing epoxy resins, epoxidised oils,    acrylic polymers and acrylic grafted polymers in which the acrylic    component contains pendent epoxy groups. Some of the acrylic acid    may be replaced by other acids, both ethylenically unsaturated and    saturated, so as to impart specific properties e.g. aliphatic acids,    fatty acids and aromatic acids.

These products may alternatively be prepared by the reaction of acarboxylic acid functional component (e.g. polyesters and acrylicpolymers) with a second component containing both epoxy groups andethylenic unsaturation e.g. glycidyl acrylate.

2—Urethane acrylates are those products formed by the reaction of anisocyanate containing component with a hydroxyl containing component. Atleast one of these components must contain ethylenic unsaturation.Examples of isocyanate functional components are hexamethylenediisocyanate, isophorone diisocyanate, isocyanate functional acrylicpolymers and polyurethanes, reaction products of hydroxyl functionalcomponents (e.g. poly-ethylene glycol, poly-propylene glycol and di-,tri- and higher hydroxy functionality aliphatic alcohols (e.g. glyceroland trimethylolpropane) and their ethoxylated, propoxylated andpolycaprolactone analogs) with di-, tri-and etcisocyanates (e.g.hexamethylene diisocyanate, isophorone diisocyanate and toluenediisocyanate (TDI)). Examples of hydroxy containing ethylenicallyunsaturated components are hydroxyethyl acrylate and its ethoxylated,propoxylated and polycaprolactone analogs

3—Multi-functional acrylate monomers are acrylic acid esters of di-,tri- and higher hydroxy functionality alcohols: e.g. polyethyleneglycol, polypropylene glycol, aliphatic diols, neopentyl glycol,ethoxylated bisphenol A, trimethylolpropane, pentaerythritol, glycerol,di-trimethylolpropane, hydroxyl functional polyesters, dipentaerythritoland the ethoxylated, propoxylated and polycaprolactone analogs of allthe above.

4—Amine-acrylate adducts are those products prepared by the partial“Michael Type Addition” of primary and secondary amines to ethylenicunsaturation i.e. the double bond of acrylate containing compounds. Ofparticular interest here are the multi-functional (meth)acrylatemonomers as mentioned above. Examples of amine-acrylate adducts arediethylamine modified trimethylolpropane triacrylate and ethanolaminemodified ethoxylated trimethylolpropane triacrylate.

5 to 8—Multifunctional acrylates of type 5 to 8 are considered as wellknown to a man skilled in the art, but some specifications are givenhere for a better illustration.

Polyester acrylates may be the reaction products of polyester polyolswith acrylic acid. Polyalkoxylated polyolacrylates or polyetheracrylates may be obtained by reacting acrylic acid with respectivelypolyalkoxylated (ethoxylated or/and propoxylated) polyols or polyetherpolyols (for example polyether based on ethoxy or/and propoxy repeatingunits). Acrylated acrylic oligomers may be the reaction products ofacrylic oligomeric copolymers bearing epoxy groups (derived for examplefrom glycidyl methacrylate) with acrylic acid. Acrylated oligomers ofSMA or of S (M) AA may be obtained by at least partial esterification ofanhydride or acid groups by an hydroxy alkyl acrylate (C₂-C₈ alkyl) . Asan example of acrylated SMA we may mention the SARBOX® resins ofSARTOMER.

All of the above listed acrylates may incorporate specific hydrophiliccomponents to facilitate their being dissolved, emulsified or dispersedin an aqueous phase. Examples are the addition of secondary amines,phosphoric acid and anhydrides (e.g. succinic anhydride, phithalicanhydride and tetrahydrophthalic anhydride). The resulting tertiaryamines and pendent carboxylic acid groups are then neutralised. Anotherhydrophilic group of particular interest is polyethylene glycol.

A particularly preferred multifunctional acrylate is ethoxylatedtrimethylolpropane triacrylate (Sartomer® 454 from Sartomer-Cray ValleyPhotocure) .

The solids content of the novel aqueous composition can be adjusted togive the desired viscosity. In general, the solids content is from 20 to80, in particular from 20 to 70, % by weight. The particle size of thedispersion may vary from 50 to 150 nm.

The minimum film forming temperature (MFFT) of the novel aqueouscomposition is preferably<10° C., more preferably<7° C. That means thatno coalescent agents are needed for the film formation at thetemperatures usually encountered in the industrial radiation curingapplication lines.

The novel dispersions are particularly suitable as binders for coatingsand coating material. Such coating compositions may contain furtheradditives, for example pigments, dyes, fillers and assistantsconventionally used in coating technology.

For radiation curing by UV light, photoinitiators are added to thedispersions. For curing by Electron Beam radiation no photoinitiator isrequired.

Examples of suitable photoinitiators are benzophenone,alkylbenzophenones, halomethylated benzophenones, Michler's ketone,2-hydrozyacetophenone and halogenated benzoohenones. Benzoin and itsderivatives are also suitable. Other effective photoinitiators areanthraquinone and many of its derivatives, for example,β-methylanthraquinone, tert-butylanthraquinone andanthraquinonecarboxylic esters and in particular acylphosphine oxides,eg. Lucirin® TP0 and Trgacure® B19.

The photoinitiators, depending on the intended use of the novelmaterials, may be used in amounts of from 0.1 to 15, preferably from 0.1to 5, % by weight, based on the polymerizable components, and can beused as an individual substance or, owing to the frequent advantageoussynergistic effects, also in combination with one another.

Advantageous additives which may lead to a further increase in thereactivity are certain tertiary amines, eg. N-methyldiethanolamine,triethylamine and triethanolamine as well as certain acrylated tertiaryamines, eg. Craynor® 386 (Sartomer-Cray Valley Photocure).

The aqueous coating compositions may contain a thermal initiator if thecoating is cured by heat or a catalyst if the coating is cured byauto-oxidation (redox mechanism). The thermal initiator is added to thecomposition from about 0.5% by weight of total non-volatiles (solidscontent) to about 2% by weight of total non-volatiles (solids content).Useful thermal initiators include azo compounds, such asazobisisobutyronitrile and the like, organic peroxides such as ketoneperoxides, hydroperoxides, alkyl peroxides, acryl peroxides, peroxyesters and the like. Useful catalysts for auto-oxidative curing includethe salts of cobalt, such as cobalt acetate, cobalt naphtenate and thelike. Thermal initiators may be particularly useful for more efficientcuring of coatings on substrates with surfaces or thicknesses presentinginaccessible zones or zones of low access to radiation curing. A thermalinitiator may also be present alone for specific applications. In such acase, the thermal curing is applied under forced temperature conditionsup to a temperature of 100° C., using for example iR (Infrared) orconvection tunnels.

Another object of the invention concerns a process for preparing acomposition according to the invention, comprising the step of mixing anaqueous dispersion of polymer (A), previously added with a volatile basein conditions to convert the said acetoacetoxy functions into enamineones, with an aqueous predispersion of (B).

An additional subject concerns an aqueous coating composition comprisingas a binder at least one aqueous composition defined according to theinvention.

The novel aqueous polymer dispersion compositions can be used as aqueousbinders for the production of industrial coatings.

These industrial coatings are used in the field of industrial woodfinishing, joinery, wood and plastics coating and in inks. They can beapplied with good adherence to substrates such as metal, plastic, glass,wood, paper, board, leather or textile, for example by spraying,pouring, roller coating, curtain coating, printing or knife coating.

More preferably the compositions of the present invention are curableafter coating the said composition, by exposure of the said coating toradiation (UV/EB). For the step of radiation curing, the coatings aregenerally pre-heated for up to 30 minutes at up to 100° C. Some of theacetoacetoxy functional groups coming from the dispersed polymer whichare blocked in the enamine form are released as the volatile baseevaporates and they can react with a part of the acrylic double bonds ofthe multifunctional acrylate to give a Michael adduct. This secondarycuring mechanism gives tack-free films before radiation curing.Afterwards the coatings are exposed for a short time to UV radiation orhigh energy electron radiation. The UV or electron radiation sourcesusually employed for curing coatings are used for this purpose.

More particularly a dual cure process for coating a substrate sureacecomprises the following consecutive steps of:

-   (a) applying an aqueous coating composition of the invention to the    substrate surface;-   (b) pre-drying the coating to evaporate water and the volatile base    by heating the said coating at a temperature in the range up to 100°    C.; and-   (c) curing the said coating by exposing it to radiation.

The present invention does also concern coated substrates obtained byusing the coating compositions as defined accordingly.

The coatings obtained after UV curing have good sanding, good adherenceto the substrate, high hardness and very good resistance to chemicals,this high performance being the result of the combination of two curingmechanisms: the one taking place before the radiation curing and thecrosslinking of the remaining acrylic double bonds during the radiationexposure.

EXAMPLES Example 1

The aqueous dispersion used contained:

-   (A) 87% by weight of a polymer of    -    25% by weight of butyl-methacrylate;    -    48% by weight of methyl-methacrylate;    -    25% by weight of acetoacetoxyethyl-methacrylate; and    -    2% by weight of acrylic acid;    -    with a Tg of polymer (A): 54° C. (calculated according to Fox        equation)-   (B) 13% by weight of a predispersion at 75% by weight of ethoxylated    (3 ethoxy units) trimethylolpropane triacrylate (Sartomer® 454 from    Sartomer-Cray Valley Photocure) prepared by adding 75 parts by    weight of the multifunctional acrylate to a solution of 3 parts by    weight of sodium dioctyl sulphosuccinate in 22 parts by weight of    deionized water.

The dispersion has

-   a solid content of 39.3%-   a viscosity of 15.7 mpa.s (Brookfield LVT, 1/60 at 25° C.);-   a pH of 8.61;-   a particle size of 71.8 nm (Zetasizer 3000) ; and-   a MFFT (Minimum Film Forming Temperature) of 6.3° C.

Example 2

The aqueous dispersion used contained:

-   (A) 81% by weight of a polymer of    -   69% by weight of methyl-methacrylate;    -   4% by weight of butyl acrylate;    -   25% by weight of acetoacetoxyethyl-methacrylate and    -   2% by weight of acrylic acid;    -   with a Tg of polymer (A) of 67° C. (conditions as for Example 1)-   (B) 19% by weight of a predispersion at 75% by weight of ethoxylated    (3 ethoxy units) trimethylolpropane triacrylate (Sartomer 454® from    Sartomer-Cray Valley Photocure) prepared in a similar manner to the    one described in the Example 1.

The dispersion has

-   a solid content of 91.4%-   a viscosity of 23.5 mPa.s (Brookfield LVT, 1/60 at 25° C.);-   a pH of 8.52;-   a particle size of 71.2 nm (Zetasizer 3000); and-   a MFFT of 0° C.

Comparative Example 1

The aqueous dispersion used contained:

-   (A) 87% by weight of a polymer of    -   55% by weight of butyl-methacrylate;    -   43% by weight of methyl-methacrylate; and    -   2% by weight of acrylic acid;    -   with a Tg of polymer (A) of 53° C. (conditions as for Example        1).-   (B) 13% by weight of a predispersion at 75% by weight of ethoxylated    (3 ethoxy units) trimethylolpropane triacrylate (Sartomer 454® from    Sartomer-Cray Valley Photocure) prepared in a similar manner to the    one described in the Example 1.

The dispersion has

-   a solid content of 40.1%;-   a viscosity of 22.5 mPa.s (Brookfield LVT, 1/60 at-   25° C.);-   a pH of 8.83-   a particle size of 75.9 nm (Zetasizer 3000) ; and-   a MFFT of +8.5° C.    Procedure

The component (A) of the EXAMPLES 1-2 and the COMPARATIVE EXAMPLE 1 havebeen prepared by a multistage polymerization system, dividing themonomer content in 2 different parts, in a ratio of 30/70, withdifferent Tgs, monomer polarity and different distribution of theacetoacetoxyethyl methacrylate, according to the specifications given inthe Table 1 inserted below. TABLE 1 EXAMPLES MONOMER COMPOSITION 1 2Comp. 1 CORE (% over total monomer of A) 30 30 30 MONOMER %: % of A %core % of A % core % of A % core BUTYL-METHACRYLATE 3.90 13 — — 12.90 43METHYL-METHACRYLATE 18.00 60 21.90 73 16.50 55 AAEM 7.50 25 7.50 25 — —ACRYLIC ACID 0.60 2 0.60 2 0.60 2 TG (Fox eq.), ° C. 64 75.75 63 SHELL(% over total monomer of A) 70 70 70 MONOMER %: % of A % shell % of A %shell % of A % shell BUTYL-METHACRYLATE 21.00 30 — — 42.00 60METHYL-METHACRYLATE 30.10 43 47.60 68 26.60 38 BUTYL ACRYLATE — — 3.50 5— — AAEM 17.50 25 17.50 25 — — ACRYLIC ACID 1.40 2 1.40 2 1.40 2 TG (Foxeq.), ° C. 49.8 66.2 49

The quantities are expressed for 100 parts of total monomer.

-   1—An initial charge containing 86.6 parts of deionised water and 5.6    parts of a 30% solution of disodium ethoxylated alcohol half ester    of sulfosuccinic acid, was put in the reactor and heated to 80° C.-   2—Once the initial charge had reached 80° C., the initial initiator    solution (1.15 parts of water and 0.05 parts of sodium persulphate)    was added.-   3—After this, the first 30% of the monomers was added, in a constant    rate during 1 hour, increasing the temperature to 84° C.-    At the sane time, the initiation feeding (5.77 parts of water and    0.4 part of sodium, persulphate) was started. Added at a constant    rate during 4 h 45 mn.-   4—When finished first part of monomers, the reactor is maintained 30    minutes at 84° C.-   5—A second part of monomers (70% of the total) is added to the    reactor in preemulsion form with 20.8 parts of water and 7 parts of    a 30% solution of disodium ethoxylated alcohol half ester of    sulfosuccinic acid.-    Time of feeding: 2 hours. The temperature is kept at 84° C. for 30    minutes more after finished the preemulsion.-   6—A redox treatment composed by 0.1 part of tertiobutyl    hydroperoxide (TBHP) and 0.1 part of sodium-formaldehyde-sulfoxylate    (SFS) disolved in 2.3 parts of water, was added in 15 minutes, and    maintained for 30 minutes more at 84° C.-   7—The reactor was cooled to 55-60° C. before starting the    neutralization step by adding in 15 minutes, a mixer of 2.08 parts    of water and 2.08 parts of ammonia 25% until a constant pH of    8.0-8.2.-   8—The reactor was cooled to below 40° C. before adding antifoam and    biocide.    Application

The dispersions prepared were mixed with 1.7% by weight, based on thesolid, of Irgacure® 184 (Ciba) . Films of 100 wet microns were appliedon glass using a doctor blade and were dried in an oven at 60° C. for 10minutes. The films obtained were dry, clear and non tacky except for theone of the COMPARATIVE EXAMPLE 1 which was tacky. They were then exposedunder a high pressure mercury lamp (80 W/cm) on a conveyor belt at abelt speed of 10 m/min (300 mJ/sqm of total UV dose).

Persoz hardness was measured before and after UV exposure. The followingresults were obtained TABLE 2 Persoz hardness (seconds) COMPARATIVEEXAMPLE 1 EXAMPLE 2 EXAMPLE 1 Before UV 99 134 88 Exposure After UVexposure 251 265 149

The coatings were also applied on wood (beech veneer). 2 coats of 80g/sqm were applied by the following method:

-   1^(st) coat of 80 g/m²-   Drying in oven for 10 minutes at 60° C.+UV curing-   Sanding-   2^(nd) coat of 80 g/m²-   Drying in oven for 10 minutes at 60° C.+UV curing UV curing was    performed using the same method as for the applications on glass.

The properties of the coatings after UV exposure are summarized in TABLE3: TABLE 3 COMPARATIVE EXAMPLE 1 EXAMPLE 2 EXAMPLE 1 SANDABILITY* 5 5 2CHEMICAL RESISTANCES (EN-12720)*: Water (16 h) 5 5 5 Water/ethanol 5 5 51:1 (16 h) Ethanol (16 h) 5 4 4 Coffee (16 h) 5 4 4 Ammonia at 4 5 1 10%in water (16 h) DBP** (16 h) 4 5 1 MEK*** (16 h) 4 4 1 Hand cream (16 h)5 5 2*the best value is 5**DBP: Dibutyl phthalate***MEK: Methyl Ethyl Ketone

1. An aqueous polymer dispersion composition comprising for 100 parts byweight of (A)+(B): (A) from 30 to 99 parts by weight of at least onedispersed polymer containing acetoacetoxy-type functional moieties, thesaid polymer having a glass transition temperature from 0 to 100° C.;and (B) from 1 to 70 parts by weight of a multifunctional acrylate, saidaqueous composition further containing a volatile base in an amountsufficient to convert the acetoacetoxy functionalities of (A) intoenamine ones.
 2. An aqueous composition as defined in claim 1 whereinthe volatile base is ammonia.
 3. An aqueous composition as defined inclaim 1 wherein the pH of said composition is higher than 7.5 and up to10.
 4. An aqueous composition as defined in claim 1 wherein theacetoacetoxy-type functional moieties are derived from acetoacetoxyethylmethacrylate monomer incorporated in the polymer (A) by an emulsionpolymerization process.
 5. An aqueous composition as defined in 4 claim1 wherein the multifunctional acrylate (B) is the ethoxylatedtrimethylolpropane triacrylate.
 6. An aqueous composition as defined inclaim 1 with a MFFT<10° C.
 7. A process for preparing a composition asdefined in claim 1 comprising mixing an aqueous dispersion of polymer(A), previously added with a volatile base under such conditions toconvert the said acetoacetoxy functions into enamine ones, with anaqueous pre-dispersion of (B).
 8. An aqueous coating compositioncomprising as a binder at least one aqueous composition as defined inclaim
 1. 9. An aqueous composition according to claim 8 furthercomprising at least one of a photoinitiator, a thermal initiator or acatalyst for auto-oxidative curing.
 10. A dual cure process for coatinga substrate surface, which comprises the consecutive steps of: (a)applying an aqueous coating composition, as defined in claim 9 to thesaid surface; (b) pre-drying the coating to evaporate water and thevolative base by heating the said coating at a temperature in the rangeup to 100° C.; and (c) curing the said coating by exposing it toradiation.
 11. An aqueous coating composition as defined in claim 8adapted for use as an aqueous binder for industrial coatings in thefield of industrial wood finishing, joinery, wood and plastics coating,floor polish or inks.
 12. An aqueous coating composition as defined inclaim 11 wherein the industrial coatings are applicable or applied tosubstrates selected from metal, plastic, glass, wood, paper, board,leather, textile, concrete, stone and derivatives.
 13. Coated substratesresulting from use according to claim
 12. 14. An aqueous composition asdefined in claim 1 wherein the acetoacetylated polymer (A) has a contentof acetoacetoxy functions from 0.14 to 1.87 expressed in mmol per gramof polymer (A).
 15. An aqueous coating composition comprising as abinder at least one aqueous composition as defined in claim
 8. 16. Adual cure process for coating a substrate surface of claim 10, whichcomprises the consecutive steps of: (a) applying an aqueous coatingcomposition, as defined in claim 10 to the said surface; (b) pre-dryingthe coating to evaporate water and the volative base by heating the saidcoating at a temperature in the range up to 100° C.; and (c) curing thesaid coating by exposing it to radiation.